Abstract: 5.5 mm thick LD10CS (2014-T6) aluminum alloy plates were TIG welded with two different processes,and the welding thermal cycle was measured by thermocouples. The effect of thermal cycle on microstructure and mechanical properties of the two joints was analyzed by optical microscopy,microhardness test and tensile test. Since the heat affected zone in the two-sided three layers welding joint undergone three thermal cycles, resulting in the hardness of the over aging zone drop significantly and tensile fracture occurred there. While each layer in the weld area experienced different thermal processes,leading to the hardness fluctuation seriously. Compared with the two-sided three layers welding,the joint of single-sided two layers welding has higher tensile strength,which is 358.3 MPa,and the width of the HAZ is narrower and the hardness in the over aging zone is higher than three layers welding joint. But due to the existing of pores and network-like distribution of secondary phase along the grain boundaries,the plasticity of the joint decreases.